Integration of IGCC plant with superconducting power island

ABSTRACT

A cooling system for high temperature superconductor equipment comprising a cryocooler in heat exchange relationship with the high temperature superconductor equipment, and an air separation unit in heat exchange relationship with the cryocooler, the system arranged such that heat from the high temperature superconductor equipment is rejected to said air separation unit via the cryocooler.

This invention was made with Government support under contract number DE-FC36-02GO11100 awarded by U.S. Department of Energy. The Government has certain rights in the invention.

BACKGROUND OF THE INVENTION

This invention relates generally to the cooling of equipment utilizing superconductors and more specifically, to the linking of a cyrocooler for high temperature superconductors with an air separation unit in a power generation plant.

One of the fundamental problems presented by various equipment that utilize superconductors is that the superconductors must be kept within a strict cryogenic temperature range so that the superconductors remain in a superconducting state. If, for example, the temperature is increased above the critical range even briefly, heat is generated within the superconducting wire that could cause further increases in temperature and perhaps lead to equipment failure.

Cryocoolers capable of cooling at temperatures between 4.2 K and 77 K have long been available. However, it is insufficient to simply achieve the operating temperature range. The cryocooler must also be capable of removing heat for a given application (its cooling capacity in watts). In this regard, removing 10 watts at 30 K is much easier than removing 500 watts at the same temperature. Moreover, depending on the thermodynamic cycle being used, a 500 watt heat load could be merely difficult or practically impossible to remove.

Users of power equipment expect that equipment to be extremely reliable. Typical allowances for unreliability for a complete turbine-generator limit the generator to only eight hours downtime each year. Each component within the generator must be even more reliable so that the entire generator achieves the stated goal. As applied to a cryocooler, the reliability budget for the equipment forces the use of redundant systems and equipment that allows online maintenance to avoid unnecessary downtime. As a result, reliability brings both complexity and cost to the cryocooler.

It is now generally known that superconducting equipment can be used in power stations. The equipment presently includes power cables, transformers, generators, fault current limiters and the like. Given that each of these components employs superconducting materials at some cryogenic temperature, and that production of coolants at cryogenic temperatures can be expensive and perhaps unreliable, a means is desired whereby cooling capacity at temperatures between, for example, liquid helium and liquid nitrogen is readily available at an economical cost.

BRIEF DESCRIPTION OF THE INVENTION

In an exemplary embodiment of this invention, a cryocooler for high temperature superconductors (HTS) is used that links into the basic process for creating relatively pure oxygen in an integrated gasification combined cycle (IGCC) power plant.

Coal gasification processes convert solid coal into synthetic gas, primarily CO and H₂. Typically, O₂ is used as the oxidizing medium. In an 1GCC plant, a cryogenic air separation unit (ASU) is often used to provide pure oxygen to the gasification reactor, often using or supplemented by, post-compression air bleed from the gas turbine. The ASU typically produces nitrogen and oxygen in the range of 63-90 K, depending on the point within the cycle being considered, and at mass flow rates that are very high compared to the cooling requirements of HTS equipment. The typical cryocooler for HTS applications operates between room temperature (25° C.) and the HTS operating temperature which may be between 30 K and 77 K. For example, in a generator, the HTS field winding may operate at 30 K while in an underground power cable, the HTS wires could be bathed in liquid nitrogen at 77 K. The key technology in known cryocoolers is the transfer of heat from the very cold cryogenic region to ambient air or other heat sinks at room temperature.

In accordance with this invention, however, the HTS cryocooler is modified so that the thermodynamic cycle operates between the desired HTS wire temperature and a heat sink much closer in temperature to the wire compared to room temperature. This is done by linking the cryocooler into the air separation process, reducing the complexity and capital cost of the cryocooler without sacrificing operating reliability.

Compared to existing cryocoolers that operate between an ambient temperature of 25° C. and a working temperature of 30 K, the heat sink for the cryocooler in the example embodiment is approximately 77 K. The reduction in the “apparent” ambient temperature allows the cryocooler to be simpler, less expensive and more reliable. In addition, it consumes less power, thereby improving the efficiency advantage of the HTS equipment.

In one exemplary embodiment, the cryocooler is based on a Reverse Brayton cooling cycle. Specifically, cold fluid from the ASU enters a reservoir available to the cryocooler and cools a separate fluid circulating between the cryogenic reservoir and a recuperative heat exchanger in the cryocooler. A separate fluid circulates between the recuperative heat exchanger and the HTS equipment. By rejecting heat from the HTS equipment to the cryogenic reservoir at a temperature of 63-90 K, instead of to a traditional heat sink at room temperature, i.e., 25° C. (or 298 K), the complexity of the cryocooler can be reduced along with capital cost.

In a second exemplary embodiment, the ASU may be linked with an otherwise conventional Gifford-McMahon (GM) cryocooler. In this embodiment, a pair of auxiliary heat exchangers is inserted in the links from the GM cryocoder compressors. One side of these heat exchangers is fed from the compressor and the other side from nitrogen lines from the ASU.

In a third exemplary embodiment, nitrogen (gaseous or liquid) or liquefied air, which is to a large extent a by-product of the ASU cycle, is simply supplied as the primary coolant to the HTS equipment. The connection between the ASU and HTS equipment can be through insulated piping or via dewars (in the case of liquid coolants) that are filled by the ASU and moved as needed to the HTS equipment.

Accordingly, in one aspect, the present invention relates to a cooling system for high temperature superconductor equipment comprising a cryocooler in heat exchange relationship with the high temperature superconductor equipment, and an air separation unit in heat exchange relationship with the cryocooler, said system arranged such that heat from the high temperature superconductor equipment is transferred to said air separation unit via the cryocooler.

In another aspect, the invention relates to a cooling system for high temperature superconductor equipment comprising a cryocooler in heat exchange relationship with the high temperature superconductor equipment, and an air separation unit in heat exchange relationship with the cryocooler, the system arranged such that heat from the high temperature superconductor equipment is transferred to the air separation unit via the cryocooler, wherein the cryocooler includes a first heat exchanger and wherein a cryogenic fluid utilized in the air separation unit passes in heat exchange relationship with gaseous helium or neon from the high temperature superconductor equipment in the first heat exchanger, wherein the air separation unit includes a second heat exchanger, and wherein the cryogenic fluid passes in heat exchange relationship with said gaseous helium or neon in the second heat exchanger, and further wherein the gaseous helium or neon is compressed in a compressor upstream of the first heat exchanger and expanded in an expansion turbine downstream of the first heat exchanger.

In still another aspect, the invention relates to a method of cooling high temperature superconductor equipment comprising (a) integrating cooling hardware of the high temperature superconductor equipment with an air separation unit of an integrated gasification combined-cycle power plant, and (b) transferring heat from the high temperature superconductor equipment to fluid in the air separation unit.

The invention will now be described in connection with the drawings identified below.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of a Reverse Brayton-type cryocooler connected between a cryogenic reservoir of an air separation unit in an IGCC plant and equipment utilizing high temperature superconductors in accordance with a first exemplary embodiment;

FIG. 2 is a schematic diagram of a Gifford-McMahon cycle cryocooler connected between an air separation unit in an IGCC plant and equipment utilizing high temperature superconductors in accordance with a second exemplary embodiment; and

FIG. 3 is a schematic diagram of an arrangement where the equipment utilizing high temperature superconductors is cooled directly by fluid from an air separation unit in accordance with a third exemplary embodiment.

DETAILED DESCRIPTION OF THE INVENTION

The exemplary embodiments describe different arrangements for using a cryocooler for high temperature superconductors that links into the basic process for creating relatively pure oxygen in an IGCC power plant. FIG. 1 illustrates an arrangement 10 utilizing a Reverse Brayton cooling cycle cryocooler. This arrangement includes an otherwise conventional cryocooler 12 fluidly connected to a cryogenic reservoir 14 of an air separation unit (ASU) 16 that is incorporated into an IGCC plant 17 and that supplies pure oxygen (02) thereto. In this arrangement, cold fluid enters the reservoir 14 via line 18 and exits through the reservoir 14 via line 20 for return to the ASU. The fluid in this circuit (AB) is typically liquid nitrogen or liquid air at a temperature of between 63-92 K. The fluid in line 20 is slightly higher in temperature than in line A because of the heat rejected (i.e., transferred) from the cryocooler to the ASU, and at a slightly lower pressure because of the pressure losses within the reservoir 14.

By means of a separate circuit (CD), fluid cooled in the reservoir 14 enters a heat exchanger 22 in the cryocooler 12 via line 24 and flow controller 25, and returns to the reservoir 14 via line 26. The fluid in line 24 is at a temperature slightly greater than the temperatures in line 18 or 20, but less than the fluid temperature in line 26. The fluid in this circuit could also be liquid nitrogen but the circuits AB and CD are separate and discreet circuits. A separate cooling loop (EF) in the cryocooler 12 cools the HTS equipment 28, with cooling fluid from the heat exchanger 22 expanded in the turbine 30 via line 32 and returned to the heat exchanger via line 34. A valve 36 in line 38 upstream of the HTS equipment 28 provides an optional bypass in the event flow to the HTS needs to be adjusted. In this way, the heat generated in the cryocooler 12 by the HTS equipment can be rejected to the cool fluid in the ASU rather than to a relatively high (room) temperature heatsink.

FIG. 2 illustrates a second embodiment including an arrangement 40 where an air separation unit 42 for an IGCC plant 45 is linked to a Gifford-McMahon (GM) cryocooler 44 used to cool the HTS equipment 46. More specifically, liquid nitrogen (or LN₂) or liquid air from the ASU 42 is circulated to a first auxiliary heat exchanger 50 via line 48 and flow controller 49, and returned to the ASU via line 52. Approximately half of the cold liquid in line 48 is diverted to a parallel, second auxiliary heat exchanger 54 via line 56 and returned to the ASU via lines 58 and 52.

The cryogenic fluid to be cooled (gaseous helium, hydrogen, liquid nitrogen or liquid neon) leaves the HTS 46 via line 60 and is circulated through a counterflow heat exchanger 62 and a compressor 64 before passing through the first auxiliary heat exchanger 50 via line 66, and back through the counterflow heat exchanger 62. An injection valve 68 permits some bleed off of fluid from line 70 before the fluid passes in heat exchange relationship with the GM cryocooler refrigerator 72. From here, the fluid returns to the HTS equipment 46.

A separate closed loop is also established between the cryocooler 44 and the second auxiliary heat exchanger 54. Specifically, fluid from the cryocooler refrigerator 72 flows via line 74 through the cryocooler compressor 76 and then through the exchanger 54 before returning to the cryocooler refrigerator 72 via line 78. With this arrangement, heat from the HTS equipment 46 and cryocooler 44 is rejected to the ASU 42, again gaining the benefit of using the cooler heat sink of the ASU.

FIG. 3 discloses still another arrangement where heat from the HTS is rejected to the ASU. Here, nitrogen (liquid or gaseous) or liquid air from the ASU 80 for an IGCC plant 81 is supplied as the primary coolant to the HTS equipment 82. More specifically, liquid N₂, for example, flows out of the ASU 80 via line 84 through a pump and flow controller 86 in the otherwise conventional cryocooler 88 and into the HTS equipment via line 90. The liquid is returned to the ASU via line 92. This arrangement is particularly useful where the HTS equipment also uses liquid for cooling, and little effect is seen on the ASU where the liquid is returned at a slightly higher temperature.

While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not to be limited to the disclosed embodiment, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims. For example, a pulse-tube refrigerator or Sterling-cycle refrigerator may also be employed as the cryocooler in the described system. 

1. A cooling system for high temperature superconductor equipment comprising a cryocooler in heat exchange relationship with the high temperature superconductor equipment; and an air separation unit in heat exchange relationship with said cryocooler, said system arranged such that heat from said high temperature superconductor equipment is transferred to said air separation unit via said cryocooler.
 2. The cooling system of claim 1, wherein said cryocooler includes a first heat exchanger and wherein a cryogenic fluid utilized in said air separation unit passes in heat exchange relationship with gaseous fluid from said high temperature superconductor equipment in said first heat exchanger.
 3. The cooling system of claim 2, wherein said air separation unit includes a second heat exchanger, and wherein said cryogenic fluid passes in heat exchange relationship with said gaseous fluid in said second heat exchanger.
 4. The cooling system of claim 2, wherein said gaseous fluid is compressed in a compressor upstream of said first heat exchanger and expanded in an expansion turbine downstream of said fuel heat exchanger.
 5. The cooling system of claim 1 in combination with an integrated gasification combined cycle power plant, and wherein said air separation unit is arranged to supply oxygen to said integrated gasification combined cycle power plant.
 6. The cooling system of claim 1 wherein said cryocooler operates in a Reverse Brayton cooling cycle.
 7. The cooling system of claim 1, wherein a first, closed cooling circuit loop extends between said high temperature superconductor equipment and said first heat exchanger; a second closed cooling circuit loop extends between said first heat exchanger and a second heat exchanger in said air separation unit, and a third closed cooling circuit loop extends between said second heat exchanger and said air separation unit.
 8. The cooling system of claim 7 wherein said first closed cooling circuit loop circulates a cooling fluid from a group comprising gaseous helium, liquid or gaseous neon and liquid or gaseous nitrogen.
 9. The cooling system of claim 8 wherein said second closed cooling circuit circulates liquid or gaseous nitrogen.
 10. The cooling system of claim 9 wherein said third cooling circuit circulates liquid or gaseous nitrogen, or liquid air.
 11. The cooling system of claim 1 wherein said cryocooler operates in a Gifford-McMahon-cooling cycle.
 12. The cooling system of claim 11 wherein cryogenic cooling fluid from said air separation unit is connected in parallel to first and second heat exchangers, said first heat exchanger also receiving coolant from said high temperature superconductor equipment and said second heat exchanger also receiving coolant from said cryocooler.
 13. The cooling system of claim 12 including a third counterflow heat exchanger arranged to receive said coolant from said high temperature superconductor equipment upstream of said first heat exchanger, with a compressor between said first and third heat exchangers.
 14. The cooling system of claim 13 wherein said coolant from said high temperature superconductor equipment flows back through said third counterflow heat exchanger downstream of said first heat exchanger.
 15. The cooling system of claim 1 wherein cryogenic fluid cooled in said air separation unit is passed through said cyrocooler and directly to said high temperature superconductor equipment and returned to the air separation unit.
 16. The cooling system of claim 15 wherein said cyrocooler includes a pump and flow controller for supplying the cryogenic fluid to the high temperature superconductor equipment.
 17. A cooling system for high temperature superconductor equipment comprising a cryocooler in heat exchange relationship with the high temperature superconductor equipment; and an air separation unit in heat exchange relationship with said cryocooler, said system arranged such that heat from said high temperature superconductor equipment is transferred to said air separation unit via said cryocooler; wherein said cryocooler includes a first heat exchanger and wherein a cryogenic fluid utilized in said air separation unit passes in heat exchange relationship with gaseous helium or neon from said high temperature superconductor equipment in said first heat exchanger; wherein said air separation unit includes a second heat exchanger, and wherein said cryogenic fluid passes in heat exchange relationship with said gaseous helium or neon in said second heat exchanger; and further wherein said gaseous helium or neon is compressed in a compressor upstream of said first heat exchanger and expanded in an expansion turbine downstream of said first heat exchanger.
 18. A method of cooling high temperature superconductor equipment comprising: (a) integrating cooling hardware of the high temperature superconductor equipment with an air separation unit of an integrated gasification combined-cycle power plant; and (b) transferring heat from the high temperature superconductor equipment to fluid in the air separation unit.
 19. The method of claim 18 wherein said cooling hardware comprises a cryocooler and wherein (b) is carried out with said cryocooler operably connected between said high temperature superconductor equipment and said air separation unit.
 20. The method of claim 19 wherein fluid in said air separation unit is between 63° and 90° K. 